Comparative Analysis of Aerobic Bacteria, Green Microalgae, and Diatoms in Domestic Wastewater Treatment: Pollutant Removal, Lipid Profile, and Biodiesel Properties

Microalgal systems are receiving significant attention for wastewater treatment because of their effective treatment performance while simultaneously generating valuable biomass for energy recovery. This study compares the performance of three biological systems - green microalgae, diatoms, and aerobic bacteria for the treatment of real domestic wastewater. Each system was operated in semi-continuous mode at different solid retention times (SRTs) of 2, 4, 6, 8, 10, and 12 days. Reactor performance was evaluated based on the removal of organic carbon, nutrients, and micropollutants. The maximum dissolved organic carbon removal efficiencies were 89% for aerobic bacteria, 84% for green microalgae, and 87% for diatoms. On the other hand, the microalgal systems outperformed the aerobic bacterial system in terms of nutrient and micropollutant removal. The microalgal systems achieved higher nutrient removal efficiencies, with maximum total nitrogen (TN) removal of 71% for green microalgae and 67% for diatoms, compared with 40% for aerobic bacteria. Diatoms exhibited a higher maximum lipid content of 21.2% at an SRT of 8 days, compared with 15.6% for green microalgae at an SRT of 6 days. Fatty acid analysis revealed the presence of palmitic, palmitoleic, stearic, and elaidic acid esters, which are suitable for biodiesel production. Overall, the results demonstrate that aerobic bacteria were effective for organic carbon removal, whereas green microalgae and diatoms exhibited enhanced nutrient and micropollutant removal while simultaneously generating lipid containing biomass with potential for biodiesel production.